The use of large reflector structures for satellite communication networks is becoming more widespread as demand for mobile communications increases. As the aperture size or number of reflectors per space-deployed communication site increases, the availability of lightweight, compactly packaged antenna structures is a key element in industry growth. A non-limiting example of an umbrella type and folded rib mesh reflector include the Tracking Data Relay System (TDRS) mesh reflector antenna system, deployed by the National Aeronautics and Space Administration (NASA). In its deployed state or condition, the metallic mesh reflector structure of the TDRS system measures 4.8 meters in diameter; yet, when folded, it is readily stowed in a cylindrical volume approximately one meter in diameter and three meters in length. Each satellite in the deployed TDRS constellation employs two such antennae.
In addition to the TDRS antenna system, there are other communications systems, such as the Asian Cellular Satellite (ACeS), that employ two mesh reflectors, each having an aperture size of twelve meters. Each of these reflectors, with folding ribs, is sized to fit within a cylindrical volume approximately one meter diameter and four and one-half meters in length. By folding the ribs, the same TDRS-configured volume, moderately lengthened, can package a reflector that is more than twice the TDRS size.
There are other reflector designs in which rigid elements are oriented in either a radial direction from the reflector center or a circumferential direction at the reflector periphery, and may employ foldable rigid elements to improve packaging. Non-limiting examples of such prior art antenna structures include the following U.S. Pat. Nos.: 5,787,671; 5,635,946; 5,680,145; 5,574,472; 5,451,975; 5,446,474; 5,198,832; 5,104,211; and 4,989,015;
The basic architecture of such `umbrella` mesh reflector designs is diagrammatically shown in the perspective view of FIG. 1, as comprising an arrangement of radially extending ribs 10, and associated sets of circumferentially extending, mesh support cords 20 cross-connected between the ribs. When deployed from its stowed condition, this structure supports a generally mesh-configured material that serves as the intended reflective (e.g., electrically conductive, RF reflective) surface 30 of the antenna.
As shown in greater detail in the side view of FIG. 2, each set of circumferential cords 20 is organized into pairs, comprised of a front cord 21 and a rear cord 23, that are joined to one another via multiple tie cords 25 therebetween. Opposite ends of the front and rear cords 21, 23 are respectively attached to a front tie 12, and rigid rear stand-offs 14, supported by and extending generally orthogonally from the ribs 10, so that each cord set 20 is placed in tension by a pair of radial ribs 10 in a generally catenary configuration. The reflective mesh 30 is retained against the underside of the front cords 21 at their attachment points 16 with the tie cords 25. As a consequence, when the support structure is deployed, the cords sets 20 define a prescribed surface with which the attached tensioned mesh 30 conforms.
Radially outermost or `intercostal` cord sets 20RO in FIG. 1, to which the outer peripheral edge 32 of the mesh is attached, are connected to stand-offs at distal ends 13 of the ribs 10. Because of the tensioning forces acting on the cord sets and on the mesh held thereby, each intercostal cord set 20RO follows a generally `scalloped` arc 34, that is recessed radially inwardly, away from circular perimeter 35 of the surface of revolution with which the circumference of the deployed mesh surface 30 should ideally conform.
Because these scalloped arcs 34 leave (generally elliptically shaped) gap areas or openings 36 between the actual (scalloped) perimeter 34 of the deployed mesh surface 30 and the wider diameter generally circular perimeter 35 passing through the distal ends 13 of the ribs 10, the effective area of the reflective mesh 30 is generally limited to the radius to the interiormost scalloped edges of its intercostal cord sets, rather than the longer radial lengths of the ribs 10. In other words, due to the loss of reflective surface material in the scalloped gaps 36, the structure supporting the mesh surface must be increased in size (diameter). The increase is such that the resulting area of the actual mesh surface, exclusive of the scallops, is equal to the area of the desired reflector.
A first shortcoming of this conventional configuration is the increased payload associated with the larger rib lengths required to stow and deploy a given mesh surface area. Secondly, since the perimeter of the actually deployed surface is scalloped rather than circular, the additional mesh reflector material in the vicinity of the distal ends of the ribs introduces anomalies into the intended radiation profile of the antenna. Although the size of the gaps could be reduced by increasing the number of ribs (thereby placing more ribs closer together), such an approach would be self-defeating by the addition of substantial weight and volume.